The Pizza Slices and Cokes


  29) Andy and Lonnie were trying to remember how much the cokes and pizza
slices were at the corner restaurant.  Recently, they had bought 2 cokes and
5 pizza slices for $16.85; and a couple days earlier, they bought 4 cokes
and 3 pizza slices for $13.05.  What is the cost of each pizza slice and
each coke?

  For this problem, we are going to use two different variables.

        x = coke
        y = pizza slice


        2x + 5y = 16.85
        4x + 3y = 13.05

  We now want to eliminate one of the variables by multiplying the top
formula by -2, so that the x's will cancel out:

        -4x -10y = -33.70
         4x + 3y =  13.05
         ----------------
             -7y = -20.65

               y = 2.95

  Now that we know the value of y, we can plug that back into the formula
to find the value for x, as follows:

        (2x + 5y = 16.85)

        2x + 14.75 = 16.85

        2x = 2.10

         x = 1.05

        Each pizza slice is $2.95, and each coke is $1.05.